In recent years, thin client systems have been introduced in which all applications to be received, output, and displayed on a terminal device are executed by a server device and all files generated in association with this process are managed also by the server device, so as to prevent leakage of information from a terminal device of a computer and facilitate application management on the terminal side, for example.
In such thin client systems, plot data of an application program to be executed by the server device is transferred to the terminal device on the client side via a network such as a LAN (Local Area Network), and is displayed on the screen of the terminal device. Accordingly, if the amount of plot data to be processed increases, or if the number of terminal devices connected to the server device increases, the load imposed on the server device to transfer the plot data to the terminal device increases. This causes a problem such as deterioration of a response time or a great limitation on the number of terminal devices to be connected.
In this regard, there is proposed a display control technique for plot data using software, in which only a rectangular plot region containing a plot data part plotted and updated within one screen is clipped, and is further compressed as needed and transferred, thereby reducing the amount of data associated with the transfer of plot data on the computer screen and alleviating the load imposed on the server device (e.g., see Patent Document 1). However, along with an increase in definition of plot data and remarkable improvement in monitor resolution, the amount of plot data to be processed on a computer screen has been increasing. For this reason, there is a demand for further reduction in processing load without deterioration of drawing quality.    [Patent Document 1] Published Japanese Translation of PCT International Publication for Patent Application, No. 2004-503862    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2004-129099